Hey Will,
I think you will want a professional to repair this. Basically what you want to do is get the ding cleaned out and then you will layer in new pieces of balsa. A regular repair person can do it, just use 3mm pieces of balsa, laminate them together, cut to fit the hole, then add add resin and sand it to match the rail. Final step is to glass over the sanded balsa.

We have really limited repair capacities here and I doubt a repair person would be able to turn around a board repair in such a short time. You are better off to have it repaired at home....